Rach combining across multiple attempts

ABSTRACT

A mechanism is proposed to reduce overhead at the expense of increasing latency for UEs with weak link gain, while the latency for most UEs may remain the same. In one aspect of this disclosure, a UE may determine the number of attempts for transmitting a RACH signal based on one or more of path loss, the transmit power of the UE, the beam correspondence at the UE, or the power of signals received during the synchronization subframe. The UE may transmit the RACH signal in the determined number of attempts. In another aspect of the disclosure, a base station may combine signals of one or more RACH attempts to decode a RACH signal. The base station may inform a UE regarding the number of RACH subframes that the base station uses for decoding the RACH signal through a random access response message.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application Ser.No. 62/343,415, entitled “RACH COMBINING ACROSS MULTIPLE SUBFRAMES” andfiled on May 31, 2016, which is expressly incorporated by referenceherein in its entirety.

BACKGROUND Field

The present disclosure relates generally to communication systems, andmore particularly, to a random-access channel (RACH).

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis Long Term Evolution (LTE). LTE is a set of enhancements to theUniversal Mobile Telecommunications System (UMTS) mobile standardpromulgated by Third Generation Partnership Project (3GPP). LTE isdesigned to support mobile broadband access through improved spectralefficiency, lowered costs, and improved services using OFDMA on thedownlink, SC-FDMA on the uplink, and multiple-input multiple-output(MIMO) antenna technology. However, as the demand for mobile broadbandaccess continues to increase, there exists a need for furtherimprovements in LTE technology. These improvements may also beapplicable to other multi-access technologies and the telecommunicationstandards that employ these technologies.

In millimeter wave (MMW) systems, a directional RACH (DRACH) may be usedfor initial network access. A base station may sweep across differentdirections in different time slots and wait to receive a RACH signalfrom one or more user equipments (UEs). The RACH duration may depend ona UE with the weakest link gain. Thus the overhead for the RACH may behigh.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

RACH duration may depend on a UE with the weakest link gain. Thus theoverhead for the RACH may be high. In an aspect of the disclosure, amethod, a computer-readable medium, and an apparatus are provided toreduce RACH overhead at the expense of increasing latency for UEs withweak link gain, while latency for most UEs may remain the same. Theapparatus may be a UE. The apparatus may determine the number ofattempts for a transmission of a RACH signal based on one or more ofpath loss, transmit power of the apparatus, the beam correspondence atthe apparatus, or the power of signals received during thesynchronization subframe. The apparatus may transmits the RACH signal inthe determined number of attempts.

In another aspect of the disclosure, a method, a computer-readablemedium, and an apparatus are provided. The apparatus may be a basestation. The apparatus may combine signals of one or more RACH attemptsto decode a RACH signal. The apparatus may inform a UE regarding thenumber of RACH attempts used for decoding the RACH signal through arandom access response message.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating LTE examples of a DLframe structure, DL channels within the DL frame structure, an UL framestructure, and UL channels within the UL frame structure, respectively.

FIG. 3 is a diagram illustrating an example of an evolved Node B (eNB)and user equipment (UE) in an access network.

FIG. 4 is a diagram illustrating an example of RACH combining acrossmultiple attempts in a wireless communication system.

FIG. 5 is diagram illustrating an example of a synchronization subframeused in a wireless communication system.

FIG. 6 is a diagram illustrating an example of directional PSS (DPSS) ina millimeter wave system.

FIG. 7 illustrates an example of reducing the DRACH duration by usingRACH combining across multiple attempts.

FIG. 8 is a diagram illustrating an example of combining signals of twoRACH subframes to decode a RACH signal.

FIG. 9 is a diagram illustrating another example of combining signals oftwo RACH subframes to decode a RACH signal.

FIG. 10 is a flowchart of a method of wireless communication.

FIG. 11 is a flowchart of a method of wireless communication.

FIG. 12 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 13 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 14 is a flowchart of a method of wireless communication.

FIG. 15 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 16 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, and an Evolved Packet Core (EPC) 160. The basestations 102 may include macro cells (high power cellular base station)and/or small cells (low power cellular base station). The macro cellsinclude eNBs. The small cells include femtocells, picocells, andmicrocells.

The base stations 102 (collectively referred to as Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN)) interface with the EPC 160 through backhaul links 132 (e.g.,S1 interface). In addition to other functions, the base stations 102 mayperform one or more of the following functions: transfer of user data,radio channel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160) with eachother over backhaul links 134 (e.g., X2 interface). The backhaul links134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use MIMO antennatechnology, including spatial multiplexing, beamforming, and/or transmitdiversity. The communication links may be through one or more carriers.The base stations 102/UEs 104 may use spectrum up to Y MHz (e.g., 5, 10,15, 20 MHz) bandwidth per carrier allocated in a carrier aggregation ofup to a total of Yx MHz (x component carriers) used for transmission ineach direction. The carriers may or may not be adjacent to each other.Allocation of carriers may be asymmetric with respect to DL and UL(e.g., more or less carriers may be allocated for DL than for UL). Thecomponent carriers may include a primary component carrier and one ormore secondary component carriers. A primary component carrier may bereferred to as a primary cell (PCell) and a secondary component carriermay be referred to as a secondary cell (SCell).

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ LTE and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing LTE in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network. LTE in an unlicensedspectrum may be referred to as LTE-unlicensed (LTE-U), licensed assistedaccess (LAA), or MuLTEfire.

The millimeter wave (mmW) base station 180 may operate in mmWfrequencies and/or near mmW frequencies in communication with the UE182. Extremely high frequency (EHF) is part of the RF in theelectromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and awavelength between 1 millimeter and 10 millimeters. Radio waves in theband may be referred to as a millimeter wave. Near mmW may extend downto a frequency of 3 GHz with a wavelength of 100 millimeters. The superhigh frequency (SHF) band extends between 3 GHz and 30 GHz, alsoreferred to as centimeter wave. Communications using the mmW/near mmWradio frequency band has extremely high path loss and a short range. ThemmW base station 180 may utilize beamforming 184 with the UE 182 tocompensate for the extremely high path loss and short range.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService (PSS), and/or other IP services. The BM-SC 170 may providefunctions for MBMS user service provisioning and delivery. The BM-SC 170may serve as an entry point for content provider MBMS transmission, maybe used to authorize and initiate MBMS Bearer Services within a publicland mobile network (PLMN), and may be used to schedule MBMStransmissions. The MBMS Gateway 168 may be used to distribute MBMStraffic to the base stations 102 belonging to a Multicast BroadcastSingle Frequency Network (MBSFN) area broadcasting a particular service,and may be responsible for session management (start/stop) and forcollecting eMBMS related charging information.

The base station may also be referred to as a Node B, evolved Node B(eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), or some other suitableterminology. The base station 102 provides an access point to the EPC160 for a UE 104. Examples of UEs 104 include a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a laptop, a personaldigital assistant (PDA), a satellite radio, a global positioning system,a multimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, a tablet, a smart device, a wearabledevice, or any other similar functioning device. The UE 104 may also bereferred to as a station, a mobile station, a subscriber station, amobile unit, a subscriber unit, a wireless unit, a remote unit, a mobiledevice, a wireless device, a wireless communications device, a remotedevice, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or some other suitable terminology.

Referring again to FIG. 1, in certain aspects, the UE 104/eNB 102 may beconfigured to combine (at 198) RACH signals carried by resources acrossmultiple RACH attempts in order to decode a RACH signal. The operationsperformed at 198 will be further described below with reference to FIGS.2-16.

FIG. 2A is a diagram 200 illustrating an example of a DL frame structurein LTE. FIG. 2B is a diagram 230 illustrating an example of channelswithin the DL frame structure in LTE. FIG. 2C is a diagram 250illustrating an example of an UL frame structure in LTE. FIG. 2D is adiagram 280 illustrating an example of channels within the UL framestructure in LTE. Other wireless communication technologies may have adifferent frame structure and/or different channels. In LTE, a frame (10ms) may be divided into 10 equally sized subframes. Each subframe mayinclude two consecutive time slots. A resource grid may be used torepresent the two time slots, each time slot including one or more timeconcurrent resource blocks (RBs) (also referred to as physical RBs(PRBs)). The resource grid is divided into multiple resource elements(REs). In LTE, for a normal cyclic prefix, an RB contains 12 consecutivesubcarriers in the frequency domain and 7 consecutive symbols (for DL,OFDM symbols; for UL, SC-FDMA symbols) in the time domain, for a totalof 84 REs. For an extended cyclic prefix, an RB contains 12 consecutivesubcarriers in the frequency domain and 6 consecutive symbols in thetime domain, for a total of 72 REs. The number of bits carried by eachRE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry DL reference (pilot)signals (DL-RS) for channel estimation at the UE. The DL-RS may includecell-specific reference signals (CRS) (also sometimes called common RS),UE-specific reference signals (UE-RS), and channel state informationreference signals (CSI-RS). FIG. 2A illustrates CRS for antenna ports 0,1, 2, and 3 (indicated as R₀, R₁, R₂, and R₃, respectively), UE-RS forantenna port 5 (indicated as R₅), and CSI-RS for antenna port 15(indicated as R). FIG. 2B illustrates an example of various channelswithin a DL subframe of a frame. The physical control format indicatorchannel (PCFICH) is within symbol 0 of slot 0, and carries a controlformat indicator (CFI) that indicates whether the physical downlinkcontrol channel (PDCCH) occupies 1, 2, or 3 symbols (FIG. 2B illustratesa PDCCH that occupies 3 symbols). The PDCCH carries downlink controlinformation (DCI) within one or more control channel elements (CCEs),each CCE including nine RE groups (REGs), each REG including fourconsecutive REs in an OFDM symbol. A UE may be configured with aUE-specific enhanced PDCCH (ePDCCH) that also carries DCI. The ePDCCHmay have 2, 4, or 8 RB pairs (FIG. 2B shows two RB pairs, each subsetincluding one RB pair). The physical hybrid automatic repeat request(ARQ) (HARQ) indicator channel (PHICH) is also within symbol 0 of slot 0and carries the HARQ indicator (HI) that indicates HARQ acknowledgement(ACK)/negative ACK (NACK) feedback based on the physical uplink sharedchannel (PUSCH). The primary synchronization channel (PSCH) is withinsymbol 6 of slot 0 within subframes 0 and 5 of a frame, and carries aprimary synchronization signal (PSS) that is used by a UE to determinesubframe timing and a physical layer identity. The secondarysynchronization channel (SSCH) is within symbol 5 of slot 0 withinsubframes 0 and 5 of a frame, and carries a secondary synchronizationsignal (SSS) that is used by a UE to determine a physical layer cellidentity group number. Based on the physical layer identity and thephysical layer cell identity group number, the UE can determine aphysical cell identifier (PCI). Based on the PCI, the UE can determinethe locations of the aforementioned DL-RS. The physical broadcastchannel (PBCH) is within symbols 0, 1, 2, 3 of slot 1 of subframe 0 of aframe, and carries a master information block (MIB). The MIB provides anumber of RBs in the DL system bandwidth, a PHICH configuration, and asystem frame number (SFN). The physical downlink shared channel (PDSCH)carries user data, broadcast system information not transmitted throughthe PBCH such as system information blocks (SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry demodulation referencesignals (DM-RS) for channel estimation at the eNB. The UE mayadditionally transmit sounding reference signals (SRS) in the lastsymbol of a subframe. The SRS may have a comb structure, and a UE maytransmit SRS on one of the combs. The SRS may be used by an eNB forchannel quality estimation to enable frequency-dependent scheduling onthe UL. FIG. 2D illustrates an example of various channels within an ULsubframe of a frame. A physical random access channel (PRACH) may bewithin one or more subframes within a frame based on the PRACHconfiguration. The PRACH may include six consecutive RB pairs within asubframe. The PRACH allows the UE to perform initial system access andachieve UL synchronization. A physical uplink control channel (PUCCH)may be located on edges of the UL system bandwidth. The PUCCH carriesuplink control information (UCI), such as scheduling requests, a channelquality indicator (CQI), a precoding matrix indicator (PMI), a rankindicator (RI), and HARQ ACK/NACK feedback. The PUSCH carries data, andmay additionally be used to carry a buffer status report (BSR), a powerheadroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of an eNB 310 in communication with a UE 350in an access network. In the DL, IP packets from the EPC 160 may beprovided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 375provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe eNB 310. These soft decisions may be based on channel estimatescomputed by the channel estimator 358. The soft decisions are thendecoded and deinterleaved to recover the data and control signals thatwere originally transmitted by the eNB 310 on the physical channel. Thedata and control signals are then provided to the controller/processor359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the EPC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the eNB 310, the controller/processor 359 provides RRClayer functionality associated with system information (e.g., MIB, SIBs)acquisition, RRC connections, and measurement reporting; PDCP layerfunctionality associated with header compression/decompression, andsecurity (ciphering, deciphering, integrity protection, integrityverification); RLC layer functionality associated with the transfer ofupper layer PDUs, error correction through ARQ, concatenation,segmentation, and reassembly of RLC SDUs, re-segmentation of RLC dataPDUs, and reordering of RLC data PDUs; and MAC layer functionalityassociated with mapping between logical channels and transport channels,multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs,scheduling information reporting, error correction through HARQ,priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the eNB 310 may be used by the TXprocessor 368 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 368 may be provided to different antenna 352 viaseparate transmitters 354TX. Each transmitter 354TX may modulate an RFcarrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 310 in a manner similar tothat described in connection with the receiver function at the UE 350.Each receiver 318RX receives a signal through its respective antenna320. Each receiver 318RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the EPC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

FIG. 4 is a diagram illustrating an example of RACH combining acrossmultiple attempts in a wireless communication system 400. In oneconfiguration, the wireless communication system 400 may be a millimeterwave system. In this example, the wireless communication system 400includes a UE 402 and a base station 406. In one configuration, multipleRACH attempts may be transmitted in different subframes. In oneconfiguration, multiple RACH attempts may be transmitted in differenttime slots, e.g., to convey multiple beam IDs to the base station. Thedifferent time slots may fall in different subframes or may fall in thesame subframe. In one configuration, each RACH attempt may be made at atransmission time that may be denoted by a combination of one or more ofa frame index, a subframe index, or a symbol index.

In one configuration, the UE 402 may optionally determine (at 408) thenumber of attempts for the transmission of a RACH signal (e.g., the RACHpreamble) based on one or more of path loss, configured transmit powerof the UE 402, the beam correspondence at the UE 402, or the power ofsignals received during the synchronization subframe. In oneconfiguration, for the UE 402, the transmit power of a RACH signal maybe determined by

P_RACH=min{P_CMAX(i),Preamble_Received_Target_Power+PL},

where

-   -   P_RACH is the transmit power of a RACH signal,    -   P_CMAX(i) is the configured UE transmit power for subframe    -   Preamble_Received_Target_Power may be the power level the base        station (e.g., 406) would like to receive for RACH, and    -   PL may be the downlink path loss estimate calculated by the UE        (e.g., 402), e.g., based on the received power of the beam        reference signal (BRS) signal associated with the selected beam.

In one configuration, the Preamble_Received_Target_Power may beestimated based on one or more of path loss, the transmit power of theUE, or the power of signals received during the synchronizationsubframe.

Beam correspondence may be defined as the ability of a UE (e.g., 402) todetermine a UE TX beam for the uplink transmission based on the UE'sdownlink measurement on the UE's RX beams. For example, in oneconfiguration, the UE 402 may have beam correspondence if the UE 402 isable to determine a UE TX beam for the uplink transmission based on theUE's downlink measurement on the UE's RX beams, and the UE 402 does nothave beam correspondence if the UE 402 is not able to determine a UE TXbeam for the uplink transmission based on the UE's downlink measurementon the UE's RX beams.

Effective isotropic radiated power (EIRP) is an IEEE standardizeddefinition of directional radio frequency (RF) power transmitted atequal power in all directions spherically from a theoretical pointsource. In one configuration, the EIRP of the UE 402 may be defined asthe summation of transmit power (e.g., P_CMAX(i)) and array gain of theUE. In one configuration, the array gain of the UE may be a power gainof transmitted signals that is achieved by using multiple-antennas attransmitter and/or receiver. In one configuration, the array gain of theUE may be proportional to the length of the array.

In one configuration, if the UE 402 has beam correspondence and(Preamble_Received_Target_Power+PL)≦(P_CMAX(i)+Array_Gain), the UE 402may transmit the RACH signal in one attempt. If the UE 402 has beamcorrespondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+Array_Gain), the UE 402may transmit the RACH signal in two or more attempts. In such aconfiguration, the number of transmission attempts may depend on thedifference between (P_CMAX(i)+Array_Gain) and(Preamble_Received_Target_Power+PL). For example, if the UE 402 has beamcorrespondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+Array_Gain), but(Preamble_Received_Target_Power+PL)≦(P_CMAX(i)+Array_Gain+alpha) (e.g.,alpha=3 dB), the UE 402 may transmit the RACH signal in two attempts. Ifthe UE 402 has beam correspondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+Array_Gain+alpha), but(Preamble_Received_Target_Power+PL)≦(P_CMAX(i)+Array_Gain+beta), the UE402 may transmit the RACH signal in three attempts. If the UE 402 hasbeam correspondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+Array_Gain+beta), the UE402 may transmit the RACH signal in four or more attempts.

In one configuration, if the UE 402 does not have beam correspondenceand (Preamble_Received_Target_Power+PL)≦P_CMAX(i), the UE 402 maytransmit the RACH signal in one attempt. If the UE 402 does not havebeam correspondence and (Preamble_Received_Target_Power+PL)>P_CMAX(i),the UE 402 may transmit the RACH signal in two or more attempts. In sucha configuration, the number of transmission attempts may depend on thedifference between P_CMAX(i) and (Preamble_Received_Target_Power+PL).For example, if the UE 402 does not have beam correspondence and(Preamble_Received_Target_Power+PL)>P_CMAX(i), but(Preamble_Received_Target_Power+PL)≦(P_CMAX(i)+alpha) (e.g., alpha=3dB), the UE 402 may transmit the RACH signal in two attempts. If the UE402 does not have beam correspondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+alpha), but(Preamble_Received_Target_Power+PL)≦(P_CMAX(i)+beta), the UE 402 maytransmit the RACH signal in three attempts. If the UE 402 does not havebeam correspondence and(Preamble_Received_Target_Power+PL)>(P_CMAX(i)+beta), the UE 402 maytransmit the RACH signal in four or more attempts.

In one configuration, the values of alpha and beta may be configurable.In such a configuration, the base station (e.g., 406) may optionallytransmit (at 420) the values of alpha and/or beta as a part of a systeminformation block (SIB) to enable each UE to determine the number ofattempts for transmitting a RACH signal.

The UE 402 may transmit (at 410) the RACH signal (e.g., the RACHpreamble) in the determined number of attempts to the base station 406.For example, if the determined number of attempts is one, the UE 402 maytransmit the RACH signal in one attempt. If the determined number ofattempts is two, the UE 402 may transmit the RACH signal in twoattempts. Examples of transmitting/receiving a RACH signal in multipleattempts will be described below with reference to FIGS. 8 and 9.

The base station 406 may combine (at 412) signals of one or more RACHattempts to decode the RACH signal (e.g., the RACH preamble). Forexample, the base station 406 may use a signal within a single RACHattempt to decode the RACH signal from a strong UE (e.g., the transmitpower of the UE is greater than the summation of the RACH preamblereceived target power and the path loss). The base station 406 maycombine signals of two or more RACH attempts to decode the RACH signalfrom a weak UE (e.g., the transmit power of the UE is less than thesummation of the RACH preamble received target power and the path loss).

The base station 406 may inform (at 416) the UE 402 the number of RACHattempts used for decoding the RACH signal (e.g., the RACH preamble). Inone configuration, the number of RACH attempts used for decoding theRACH signal may be transmitted in a RACH message (e.g., the randomaccess response message, also may be referred to as RACH message 2 inthe RACH procedure) to the UE 402.

In one configuration, the UE 402 may optionally adjust (at 422) thetransmission power for a RACH Message 3 (e.g., the connection requestmessage) according to the number of attempts the base station 406 usesto decode the RACH preamble. In one configuration, the UE 402 maytransmit the RACH Message 3 to the base station 406 using the adjustedtransmission power. In one configuration, to adjust the transmissionpower for the RACH message 3, the UE 402 may reduce the transmissionpower for the RACH message 3 to be lower than a threshold (e.g., lessthan the maximum transmit power of the UE 402) if the base station 406decodes the RACH preamble in one attempt. In one configuration, toadjust the transmission power for the RACH message 3, the UE 402 mayincrease the transmission power for the RACH message 3 to be higher thana threshold (e.g., higher than 90% of the maximum transmit power of theUE 402) if the base station 406 decodes the RACH preamble in two or moreattempts. In one configuration, the UE 402 may transmit the RACH Message3 using the number of attempts that the base station 406 uses to decodethe RACH preamble.

FIG. 5 is diagram illustrating an example of a synchronization subframe500 used in a wireless communication system. In this example, 1, 2, 4 or8 antenna ports may be active. The beam of each antenna port may changefrom symbol to symbol within the synchronization subframe 500. A primarysynchronization signal (PSS), an extended synchronization signal (ESS),a secondary synchronization signal (SSS), and a PBCH may be transmittedby all antenna ports on the same subcarriers. A BRS may be transmittedby all antenna ports, but either on disjoint subcarriers or are codemultiplexed. The contents of the ESS may change from symbol to symbol.Thus a UE (e.g., 402) may identify a particular symbol within thesynchronization subframe 500 based on the contents of the ESS.

FIG. 6 is a diagram 600 illustrating an example of directional PSS(DPSS) in a millimeter wave system. In one configuration, the DPSS maybe within the synchronization subframe 500 described above in FIG. 5. InFIG. 6, different TX/RX beam directions (e.g., 602, 604, . . . 608) ofmillimeter wave band are illustrated with different patterns. To enablethe UE (e.g., 402) to learn useful TX/RX beam pairs and to overcome highpath loss, beamforming is used on RX and TX. The base station (e.g.,406) sends out PSS on several successive symbols but in different beamdirections sweeping through the entire sector. For example, in eachsynchronization subframe, the PSS on symbol 0 may be in beam direction602, the PSS on symbol 1 may be in beam direction 604, . . . , and thePSS on symbol 13 may be in beam direction 608. By sending out the PSS indifferent beam directions, the UE may be able to select the best beampair for TX/RX.

FIG. 7 illustrates an example of reducing the DRACH duration by usingRACH combining across multiple attempts. Specifically, diagram 700 showsthe DRACH duration before using RACH combining across multiple attemptsand diagram 750 shows the reduced DRACH duration after using RACHcombining across multiple attempts.

The UE (e.g., 402) may select the best beam based on the received DPSSand find corresponding timing to transmit RACH signal. In oneconfiguration, the best beam may be the beam with the strongest signaland/or the least inference. In one configuration, the UE may selectsubcarrier region and cyclic shift randomly. As shown in diagram 700,the RACH duration depends on the UE with the weakest link gain. As theUE of the weakest link gain needs more time to transmit enough energyfor the RACH signal to be detected by the base station, the RACHduration may be long, thus leading to high overhead.

In one configuration, using RACH combining across multiple attempts mayreduce RACH duration by a factor of two, as illustrated in diagram 750.UEs with good link gain transmit the RACH in one attempt. UEs with poorlink gain transmit the RACH in two or more attempts. The base station(e.g., 406) may keep a memory for energy received in one or moreprevious attempts and combine received energy across two or moreattempts to provide better link budget for weak UEs.

FIG. 8 is a diagram illustrating an example of combining signals of twoRACH subframes to decode a RACH signal. At 800, the base station (e.g.,406) receives a signal 802 from a strong UE and a signal 804 from a weakUE in RACH subframe 1. In one configuration, each of the signals 802 and804 may convey at least a portion of the RACH preamble from therespective UE. A power threshold level 806 indicates the threshold levelof power in a signal after correlation of the signal with a predefinedRACH preamble in order for the base station to detect the signal.

Because the signal 802 exceeds the power threshold level 806 aftercorrelation and the signal 804 does not exceed the power threshold level806 after correlation, the base station can only detect the signal 802from the strong UE. In one configuration, the base station may find thetotal power of the RACH subframe 1 after correlation, and subtract thecorrelated power corresponding to the signal 802 to obtain an updatedpower of RACH subframe 1. In one configuration, the base station maytransmit a RACH message 2, i.e., a random access response message of acontention based random access procedure, to the corresponding beamdirection to convey whether or not the base station has decoded the RACHpreamble in one subframe. Upon reception of the RACH message 2, the weakUE may realize that the base station decoded a strong UE's RACH signalbecause the base station could not have decoded the weak UE's signal inone RACH subframe.

At 830, the base station receives a signal 832 from the weak UE in RACHsubframe 2. The base station determines the power in RACH subframe 2after correlation and adds the power to the updated power of RACHsubframe 1. After addition, a signal 852 is obtained. The signal 852 isan equivalent correlated signal after removing the energy of the strongUE and combining the power of subframes 1 and 2. The signal 852 mayexceed the power threshold level 806. Thus, the signal 852 of the weakUE can be detected by the base station.

FIG. 9 is a diagram illustrating another example of combining signals oftwo RACH subframes to decode a RACH signal. At 900, the base station(e.g., 406) receives a signal 902 from a strong UE and a signal 904 froma weak UE in RACH subframe 1. In one configuration, each of the signals902 and 904 may convey the RACH preamble from the respective UE. A powerthreshold level 906 indicates the threshold level of power in a signalafter the signal gets correlated with a RACH preamble in order for thebase station to detect that signal. Because the signal 902 exceeds thepower threshold level 906 after correlation and the signal 904 does notexceed the power threshold level 906 after correlation, the base stationcan only detect the signal 902 from the strong UE. In one configuration,the base station may ignore the remaining power of the RACH subframe 1.In one configuration, the base station may transmit a RACH message 2,e.g., a random access response message of contention based random accessprocedure, to the corresponding beam direction to convey whether or notthe base station has decoded the RACH preamble in one subframe. Uponreception of the RACH message 2, the weak UE may realize that the basestation decoded a strong UE's RACH signal because the base stationcannot decode the weak UE's signal in one RACH subframe. The weak UE mayrealize that the RACH signal may need to be transmitted in twosubsequent subframes so that the base station can decode the RACH signalfrom the weak UE.

At 920, the base station receives a signal 922 from the weak UE in RACHsubframe 2. At 940, the base station receives a signal 942 from the weakUE in RACH subframe 3. Neither the signal 922 nor the signal 942, afterbeing correlated with the RACH preamble, exceeds the power thresholdlevel 906. The base station may non-coherently combine the power ofsubframes 2 and 3 and obtain an equivalent correlated signal 960 for theweak UE, which exceeds the power threshold level 906. Thus, the basestation is able to detect the weak UE's signal by correlating thereceived signal with the RACH preamble and then combining the power ofthe correlated signals of subframes 2 and 3. In one configuration,non-coherently combining of two correlated signals may mean the basestation does not need the phase information of the correlated signals tocombine the signals. In one configuration, non-coherently combining maymean combining the amplitude of the correlated signals/power.

FIG. 10 is a flowchart 1000 of a method of wireless communication. Themethod may be performed by a UE (e.g., the UE 104, 350, 402, or theapparatus 1202/1202′). At 1002, the UE may optionally determine thenumber of attempts for a transmission of a RACH signal (e.g., the RACHpreamble) based on one or more of path loss, the configured transmitpower of the UE, the beam correspondence at the UE, or the power ofsignals received during a synchronization subframe. In oneconfiguration, the UE may have the beam correspondence when the UE isable to determine a transmit beam for uplink transmission of the UEbased on downlink measurements on receive beams of the UE. In oneconfiguration, the operations performed at 1002 may be the operationsdescribed above with reference to 408 of FIG. 4. In one configuration,the operations performed at 1002 may be the operations described belowwith reference to FIG. 11. In one configuration, the synchronizationsubframe may include one or more of primary synchronization signal,secondary synchronization signal, extended synchronization signal,physical broadcast channel, or beam reference signal.

In one configuration, multiple RACH attempts may be transmitted indifferent subframes. In one configuration, multiple RACH attempts may betransmitted in different time slots, e.g., to convey multiple beam IDsto the base station. The different time slots may be in differentsubframes or may be in the same subframe. In one configuration, eachRACH attempt may be made at a transmission time that may be denoted by acombination of one or more of a frame index, a subframe index, or asymbol index.

In one configuration, to determine the number of attempts, the UE mayestimate the RACH preamble received target power based on one or more ofthe path loss, the transmit power of the UE, or the power of the signalsreceived during the synchronization subframe. In such a configuration,the number of attempts may be determined based on one or more of thepath loss, the transmit power of the UE, the beam correspondence at theUE, or the RACH preamble received target power.

In one configuration, the determined number of attempts may be one whenthe maximum EIRP of the UE is greater than the summation of the RACHpreamble received target power, the path loss, and an offset. In oneconfiguration, the determined number of attempts may be more than onewhen the maximum EIRP of the UE is less than the summation of the RACHpreamble received target power, the path loss, and the offset. In oneconfiguration, the value of the offset may be zero when the UE has thebeam correspondence. In one configuration, the value of the offset maybe greater than zero when the UE does not have the beam correspondence.In one configuration, the offset may be determined based on theachievable array gain of the UE. In one configuration, the EIRP of theUE may be defined as the summation of the transmit power of the UE andthe array gain of the UE.

In one configuration, the path loss may be determined based on areceived signal (e.g., the BRS signal) during a synchronizationsubframe. In one configuration, the path loss may be determinedindividually for each of the multiple beams transmitted during asynchronization subframe. In one configuration, the configured transmitpower of the UE and the RACH preamble received target power may bereceived from a base station during a transmission of a SIB. In oneconfiguration, the UE may receive several threshold parameters (e.g.,alpha, beta described above with reference to FIG. 4) from the basestation during the reception of a SIB that will allow the UE todetermine the number of attempts that the base station may need fordecoding a RACH signal from the UE.

At 1004, the UE may transmit the RACH signal (e.g., the RACH preamble)in the determined number of attempts. In one configuration, theoperations performed at 1004 may be the operations described above withreference to 410 of FIG. 4.

In one configuration, the RACH signal may be a DRACH signal. In oneconfiguration, the DRACH signal may be transmitted via the best beamselected from several beams received during a synchronization subframe.In one configuration, the DRACH signal may be transmitted at atransmission time when a base station receives signal using the bestbeam. The best beam may denote a beam whose corresponding referencesignal, transmitted during a synchronization subframe (e.g., thesynchronization subframe 500), is the strongest reference signalreceived at the UE among all possible beams. In one configuration, thetransmission time for transmitting the DRACH signal may be denoted by acombination of one or more of a frame index, a subframe index, or asymbol index. In one configuration, the DRACH signal may be transmittedduring the first available RACH attempt.

At 1006, the UE may optionally receive, through a RACH message 2 (e.g.,the random access response message) from the base station, informationincluding the number of attempts the base station uses to decode theRACH preamble. In one configuration, the operations performed at 1006may be the operations described above with reference to 416 of FIG. 4.

At 1008, the UE may optionally adjust the transmission power for a RACHmessage 3 (e.g., the connection request message) according to the numberof attempts the base station uses to decode the RACH preamble. In oneconfiguration, the operations performed at 1008 may be the operationsdescribed above with reference to 422 of FIG. 4.

In one configuration, to adjust the transmission power for the RACHmessage 3, the UE may decrease the transmission power to be lower than athreshold (e.g., lower than the maximum transmit power of the UE) if thebase station decodes the RACH preamble in one attempt. In oneconfiguration, to adjust the transmission power for the RACH message 3,the UE may increase the transmission power to be higher than a threshold(e.g., higher than 90% of the maximum transmit power of the UE) if thebase station decodes the RACH preamble in two or more attempts.

At 1010, the UE may optionally transmit the RACH message 3 (e.g., theconnection request message) using the adjusted transmission power. Inone configuration, the RACH message 3 may be transmitted in the numberof attempts used by the base station to decode the RACH preamble. Forexample, if the base station decodes the RACH preamble in one attempt,the UE may transmit the RACH message 3 in one attempt; if the basestation decodes the RACH preamble in two attempts, the UE may transmitthe RACH message 3 in two attempts.

In one configuration, the information received from the base station mayfurther include the beam gain measured at the base station while theRACH preamble is received. In such a configuration, the UE may transmitthe RACH message 3 based on the received number of attempts and/or thereceived beam gain. For example, the UE may determine the number ofattempts for transmitting the RACH message 3 based on the receivednumber of attempts and/or the received beam gain.

FIG. 11 is a flowchart 1100 of a method of wireless communication. Themethod may be performed by a UE (e.g., the UE 104, 350, 402, or theapparatus 1202/1202′). In one configuration, the method may include theoperations described above with reference to 408 of FIG. 4. In oneconfiguration, the method may include the operations described abovewith reference to 1002 of FIG. 10. At 1102, the UE may determine whetherthe UE has beam correspondence. If the UE has beam correspondence, theUE may proceed to 1104. If the UE does not have beam correspondence, theUE may proceed to 1106.

At 1104, the UE may determine whether the UE's EIRP, e.g., the summationof the UE's transmit power (T) and array gain (A), is greater than orequal to the summation of the path loss (PL) and the preamble receivedtarget power (R). If (T+A)≧(PL+R), the UE may proceed to 1108. If(T+A)<(PL+R), the UE may proceed to 1110.

At 1106, the UE may determine whether the UE's transmit power (T) isgreater than or equal to the summation of the path loss (PL) and thepreamble received target power (R). If T≧(PL+R), the UE may proceed to1108. If T<(PL+R), the UE may proceed to 1110.

At 1108, the UE may determine the number of attempts for thetransmission of a RACH preamble to be one.

At 1110, the UE may determine the number of attempts for thetransmission of a RACH preamble to be more than one.

FIG. 12 is a conceptual data flow diagram 1200 illustrating the dataflow between different means/components in an exemplary apparatus 1202.The apparatus may be a UE. The apparatus 1202 includes a receptioncomponent 1204 that receives synchronization signal, SIB, and RACHmessage 2 (e.g., the random access response message) from a base station1250. In one configuration, the SIB may include the values of alpha andbeta that enables the apparatus 1202 to determine the number of attemptsfor transmitting a RACH signal, as described above with reference toFIG. 4. In one configuration, the RACH message 2 may include the numberof attempts the base station 1250 uses to decode the RACH preamble. Inone configuration, the reception component 1204 may perform operationsdescribed above with reference to 1006 of FIG. 10.

The apparatus 1202 may include a transmission component 1210 thattransmits a RACH signal (e.g., the RACH preamble or RACH message 3) tothe base station 1250. In one configuration, the transmission component1210 may perform operations described above with reference to 1004 or1010 of FIG. 10. In one configuration, the transmission component 1210may perform operations described above with reference to 1004 or 1010 ofFIG. 10. The reception component 1204 and the transmission component1210 may cooperate with each other to coordinate the communications ofthe apparatus 1202.

The apparatus 1202 may include a RACH component 1206 that determines thenumber of attempts and/or power for transmitting RACH signal andgenerates RACH signal. In one configuration, the RACH component 1206determines the number of attempts for transmitting RACH signal based onthe synchronization signal and SIB received from the reception component1204. In one configuration, the RACH component 1206 may adjust thetransmission power for a RACH message 3 based on the number of attemptsthat the base station 1250 uses to decode the RACH preamble. In oneconfiguration, the RACH component 1206 may perform operations describedabove with reference to 1002 or 1008 of FIG. 10, or 1102-1110 of FIG.11.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 10 and11. As such, each block in the aforementioned flowcharts of FIGS. 10 and11 may be performed by a component and the apparatus may include one ormore of those components. The components may be one or more hardwarecomponents specifically configured to carry out the statedprocesses/algorithm, implemented by a processor configured to performthe stated processes/algorithm, stored within a computer-readable mediumfor implementation by a processor, or some combination thereof.

FIG. 13 is a diagram 1300 illustrating an example of a hardwareimplementation for an apparatus 1202′ employing a processing system1314. The processing system 1314 may be implemented with a busarchitecture, represented generally by the bus 1324. The bus 1324 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1314 and the overalldesign constraints. The bus 1324 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1304, the components 1204, 1206, 1210, and thecomputer-readable medium/memory 1306. The bus 1324 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1314 may be coupled to a transceiver 1310. Thetransceiver 1310 is coupled to one or more antennas 1320. Thetransceiver 1310 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1310 receives asignal from the one or more antennas 1320, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1314, specifically the reception component 1204. Inaddition, the transceiver 1310 receives information from the processingsystem 1314, specifically the transmission component 1210, and based onthe received information, generates a signal to be applied to the one ormore antennas 1320. The processing system 1314 includes a processor 1304coupled to a computer-readable medium/memory 1306. The processor 1304 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1306. The software, whenexecuted by the processor 1304, causes the processing system 1314 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 1306 may also be used forstoring data that is manipulated by the processor 1304 when executingsoftware. The processing system 1314 further includes at least one ofthe components 1204, 1206, 1210. The components may be softwarecomponents running in the processor 1304, resident/stored in thecomputer readable medium/memory 1306, one or more hardware componentscoupled to the processor 1304, or some combination thereof. Theprocessing system 1314 may be a component of the UE 350 and may includethe memory 360 and/or at least one of the TX processor 368, the RXprocessor 356, and the controller/processor 359.

In one configuration, the apparatus 1202/1202′ for wirelesscommunication may include means for determining the number of attemptsfor a transmission of a RACH signal based on one or more of path loss,the transmit power of the apparatus 1202/1202′, the beam correspondenceat the apparatus 1202/1202′, or the power of signals received during thesynchronization subframe. In one configuration, the means fordetermining the number of attempts may perform operations descried abovewith reference to 1002 of FIG. 10 or 1102-1110 of FIG. 11. In oneconfiguration, the means for determining the number of attempts may bethe RACH component 1206 or the processor 1304. In one configuration, themeans for determining the number of attempts may estimate the RACHpreamble received target power based on one or more of the path loss,the transmit power of the apparatus 1202/1202′, or the power of thesignals received during the synchronization subframe.

In one configuration, the apparatus 1202/1202′ may include means fortransmitting the RACH signal in the determined number of attempts. Inone configuration, the means for transmitting the RACH signal in thedetermined number of attempts may perform operations descried above withreference to 1004 of FIG. 10. In one configuration, the means fortransmitting the RACH signal in the determined number of attempts may bethe one or more antennas 1320, the transceiver 1310, the transmissioncomponent 1210, or the processor 1304.

In one configuration, the apparatus 1202/1202′ may include means fortransmitting a RACH preamble to a base station in one or more attempts.In one configuration, the means for transmitting a RACH preamble to abase station in one or more attempts may perform operations descriedabove with reference to 1004 of FIG. 10. In one configuration, the meansfor transmitting a RACH preamble to a base station in one or moreattempts may be the one or more antennas 1320, the transceiver 1310, thetransmission component 1210, or the processor 1304.

In one configuration, the apparatus 1202/1202′ may include means forreceiving, through a random access response message from the basestation, information comprising a number of attempts the base stationuses to decode the RACH preamble. In one configuration, the means forreceiving information comprising a number of attempts the base stationuses to decode the RACH preamble may perform operations descried abovewith reference to 1006 of FIG. 10. In one configuration, the means forreceiving information comprising a number of attempts the base stationuses to decode the RACH preamble may be the one or more antennas 1320,the transceiver 1310, the reception component 1204, or the processor1304.

In one configuration, the apparatus 1202/1202′ may include means foradjusting a transmission power for a connection request messageaccording to the number of attempts the base station uses to decode theRACH preamble. In one configuration, the means for adjusting atransmission power for a connection request message according to thenumber of attempts the base station uses to decode the RACH preamble mayperform operations descried above with reference to 1008 of FIG. 10. Inone configuration, the means for adjusting a transmission power for aconnection request message according to the number of attempts the basestation uses to decode the RACH preamble may be the RACH component 1206or the processor 1304.

In one configuration, the means for adjusting the transmission power forthe connection request message may be configured to decrease thetransmission power to be lower than a threshold when the base stationdecodes the RACH preamble in one attempt. In one configuration, themeans for adjusting the transmission power for the connection requestmessage may be configured to increase the transmission power to behigher than a threshold when the base station decodes the RACH preamblein two or more attempts.

In one configuration, the apparatus 1202/1202′ may include means fortransmitting the connection request message using the adjustedtransmission power. In one configuration, the means for transmitting theconnection request message using the adjusted transmission power mayperform operations descried above with reference to 1010 of FIG. 10. Inone configuration, the means for transmitting the connection requestmessage using the adjusted transmission power may be the one or moreantennas 1320, the transceiver 1310, the transmission component 1210, orthe processor 1304.

In one configuration, the apparatus 1202/1202′ may include means fortransmitting a connection request message in the number of attempts. Inone configuration, the means for transmitting a connection requestmessage in the number of attempts may be the one or more antennas 1320,the transceiver 1310, the transmission component 1210, or the processor1304.

In one configuration, the apparatus 1202/1202′ may include means fortransmitting a connection request message based on the number ofattempts and the beam gain. In one configuration, the means fortransmitting a connection request message based on the number ofattempts and the beam gain may be the one or more antennas 1320, thetransceiver 1310, the transmission component 1210, or the processor1304.

In one configuration, the apparatus 1202/1202′ may include means forreceiving a synchronization subframe. In one configuration, the meansfor receiving a synchronization subframe may be the one or more antennas1320, the transceiver 1310, the reception component 1204, or theprocessor 1304.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1202 and/or the processing system 1314 ofthe apparatus 1202′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1314 mayinclude the TX Processor 368, the RX Processor 356, and thecontroller/processor 359. As such, in one configuration, theaforementioned means may be the TX Processor 368, the RX Processor 356,and the controller/processor 359 configured to perform the functionsrecited by the aforementioned means.

FIG. 14 is a flowchart 1400 of a method of wireless communication. Themethod may be performed by an eNB (e.g., the eNB 102, 310, 406, or theapparatus 1502/1502′). At 1402, the eNB may combine signals of one ormore RACH attempts to decode a RACH signal. In one configuration, theoperations performed at 1402 may be the operations described above withreference to 412 of FIG. 4. In one configuration, the operationsperformed at 1402 may be the operations described above with referenceto FIG. 8 or FIG. 9.

In one configuration, to combine the signal of one or more RACH attemptsto detect the RACH signal, the eNB may non-coherently add power of thesignals of the one or more RACH attempts after correlating these signalswith the RACH preamble to obtain an equivalent signal that is detectableby the eNB. In one configuration, non-coherently adding may mean the eNBdo not need the phase information of the correlated signals to combinethe power of the correlated signals. In one configuration,non-coherently adding may mean adding the amplitude of the power of thecorrelated signals. In one configuration, the RACH signal may be a DRACHsignal.

At 1404, the eNB may inform the UE, through a random access responsemessage, regarding the number of RACH attempts that the eNB uses fordecoding the RACH signal. In one configuration, the operations performedat 1404 may be the operations described above with reference to 416 ofFIG. 4. In one configuration, the random access response message may bethe message 2 in a RACH procedure.

FIG. 15 is a conceptual data flow diagram 1500 illustrating the dataflow between different means/components in an exemplary apparatus 1502.The apparatus may be a eNB. The apparatus 1502 includes a receptioncomponent 1504 that receives RACH signal from a UE 1550. The apparatus1502 may include a transmission component 1510 that transmits RACHmessage to the UE 1550. In one configuration, the transmission component1510 may perform operations described above with reference to 1404 ofFIG. 14. The reception component 1504 and the transmission component1510 may cooperate with each other to coordinate the communications ofthe apparatus 1502.

The apparatus 1502 may include a RACH decoding component 1506 thatdecodes RACH signal by combining signals of one or more RACH attempts.In one configuration, the RACH decoding component 1506 may performoperations described above with reference to 1402 of FIG. 14.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowchart of FIG. 14. Assuch, each block in the aforementioned flowchart of FIG. 14 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 16 is a diagram 1600 illustrating an example of a hardwareimplementation for an apparatus 1502′ employing a processing system1614. The processing system 1614 may be implemented with a busarchitecture, represented generally by the bus 1624. The bus 1624 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1614 and the overalldesign constraints. The bus 1624 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1604, the components 1504, 1506, 1510, and thecomputer-readable medium/memory 1606. The bus 1624 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1614 may be coupled to a transceiver 1610. Thetransceiver 1610 is coupled to one or more antennas 1620. Thetransceiver 1610 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1610 receives asignal from the one or more antennas 1620, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1614, specifically the reception component 1504. Inaddition, the transceiver 1610 receives information from the processingsystem 1614, specifically the transmission component 1510, and based onthe received information, generates a signal to be applied to the one ormore antennas 1620. The processing system 1614 includes a processor 1604coupled to a computer-readable medium/memory 1606. The processor 1604 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1606. The software, whenexecuted by the processor 1604, causes the processing system 1614 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 1606 may also be used forstoring data that is manipulated by the processor 1604 when executingsoftware. The processing system 1614 further includes at least one ofthe components 1504, 1506, 1510. The components may be softwarecomponents running in the processor 1604, resident/stored in thecomputer readable medium/memory 1606, one or more hardware componentscoupled to the processor 1604, or some combination thereof. Theprocessing system 1614 may be a component of the eNB 310 and may includethe memory 376 and/or at least one of the TX processor 316, the RXprocessor 370, and the controller/processor 375.

In one configuration, the apparatus 1502/1502′ for wirelesscommunication includes means for combining signals of one or more RACHattempts to decode a RACH signal. In one configuration, the means forcombining signals of one or more RACH attempts to decode a RACH signalmay perform operations descried above with reference to 1402 of FIG. 14.In one configuration, the means for combining signals of one or moreRACH attempts to decode a RACH signal may be the RACH decoding component1506 or the processor 1604. In one configuration, the means forcombining the signals of the one or more RACH attempts may be configuredto non-coherently add power of the signals of the one or more RACHattempts.

In one configuration, the apparatus 1502/1502′ may include means forinforming a UE regarding the number of RACH attempts used for decodingthe RACH signal through a random access response message. In oneconfiguration, the means for informing a UE regarding the number of RACHattempts used for decoding the RACH signal through a random accessresponse message may perform operations descried above with reference to1404 of FIG. 14. In one configuration, the means for informing a UEregarding the number of RACH attempts used for decoding the RACH signalthrough a random access response message may be the one or more antennas1620, the transceiver 1610, the transmission component 1510, or theprocessor 1604.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1502 and/or the processing system 1614 ofthe apparatus 1502′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1614 mayinclude the TX Processor 316, the RX Processor 370, and thecontroller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication of a userequipment (UE), comprising: determining a number of attempts for atransmission of a random-access channel (RACH) signal based on one ormore of a path loss, a transmit power of the UE, a beam correspondenceat the UE, or a power of signals received during a synchronizationsubframe; and transmitting the RACH signal in the determined number ofattempts.
 2. The method of claim 1, wherein the UE has the beamcorrespondence when the UE is able to determine a transmit beam foruplink transmission of the UE based on downlink measurements on receivebeams of the UE.
 3. The method of claim 1, wherein the determining thenumber of attempts comprises: estimating a RACH preamble received targetpower based on one or more of the path loss, the transmit power of theUE, or the power of the signals received during the synchronizationsubframe, wherein the number of attempts is determined based on one ormore of the path loss, the transmit power of the UE, the beamcorrespondence at the UE, or the RACH preamble received target power. 4.The method of claim 3, wherein the determined number of attempts is onewhen a maximum effective isotropic radiated power (EIRP) of the UE isgreater than a summation of the RACH preamble received target power, thepath loss, and an offset, wherein the determined number of attempts ismore than one when the maximum EIRP of the UE is less than the summationof the RACH preamble received target power, the path loss, and theoffset.
 5. The method of claim 4, wherein a value of the offset is zerowhen the UE has the beam correspondence.
 6. The method of claim 4,wherein a value of the offset is greater than zero when the UE does nothave the beam correspondence.
 7. The method of claim 6, wherein theoffset is determined based on an achievable array gain of the UE.
 8. Themethod of claim 4, wherein the EIRP of the UE is defined as a summationof the transmit power of the UE and an array gain of the UE.
 9. Themethod of claim 1, wherein the path loss is determined individually foreach of a plurality of beams transmitted during the synchronizationsubframe.
 10. The method of claim 1, wherein the RACH signal is adirectional RACH (DRACH) signal, wherein the DRACH signal is transmittedat a transmission time when a base station receives signal using a bestbeam.
 11. The method of claim 10, wherein the best beam denotes a beamwhose corresponding reference signal, transmitted during thesynchronization subframe, is a strongest reference signal at the UEamong all possible beams.
 12. The method of claim 10, wherein the DRACHsignal is transmitted in the best beam selected from a plurality ofbeams received during the synchronization subframe.
 13. The method ofclaim 1, wherein each attempt is made at a transmission time denoted bya combination of one or more of frame index, subframe index, or symbolindex.
 14. A method of wireless communication of a base station,comprising: combining signals of one or more random-access channel(RACH) attempts to decode a RACH signal; and informing a user equipment(UE) regarding a number of RACH attempts used for decoding the RACHsignal through a random access response message.
 15. The method of claim14, wherein the combining of the signals of the one or more RACHattempts comprises non-coherently adding power of the signals of the oneor more RACH attempts.
 16. The method of claim 14, wherein the RACHsignal is a directional RACH (DRACH) signal.
 17. An apparatus forwireless communication, the apparatus being a user equipment (UE),comprising: a memory; and at least one processor coupled to the memoryand configured to: determine a number of attempts for a transmission ofa random-access channel (RACH) signal based on one or more of a pathloss, a transmit power of the UE, a beam correspondence at the UE, or apower of signals received during a synchronization subframe; andtransmit the RACH signal in the determined number of attempts.
 18. Theapparatus of claim 17, wherein the UE has the beam correspondence whenthe UE is able to determine a transmit beam for uplink transmission ofthe UE based on downlink measurements on receive beams of the UE. 19.The apparatus of claim 17, wherein, to determine the number of attempts,the at least one processor is configured to: estimate a RACH preamblereceived target power based on one or more of the path loss, thetransmit power of the UE, or the power of the signals received duringthe synchronization subframe, wherein the number of attempts isdetermined based on one or more of the path loss, the transmit power ofthe UE, the beam correspondence at the UE, or the RACH preamble receivedtarget power.
 20. The apparatus of claim 19, wherein the determinednumber of attempts is one when a maximum effective isotropic radiatedpower (EIRP) of the UE is greater than a summation of the RACH preamblereceived target power, the path loss, and an offset, wherein thedetermined number of attempts is more than one when the maximum EIRP ofthe UE is less than the summation of the RACH preamble received targetpower, the path loss, and the offset.
 21. The apparatus of claim 20,wherein a value of the offset is zero when the UE has the beamcorrespondence.
 22. The apparatus of claim 20, wherein a value of theoffset is greater than zero when the UE does not have the beamcorrespondence, wherein the offset is determined based on an achievablearray gain of the UE.
 23. The apparatus of claim 20, wherein the EIRP ofthe UE is defined as a summation of the transmit power of the UE and anarray gain of the UE.
 24. The apparatus of claim 17, wherein the pathloss is determined individually for each of a plurality of beamstransmitted during the synchronization subframe.
 25. The apparatus ofclaim 17, wherein the RACH signal is a directional RACH (DRACH) signal,wherein the DRACH signal is transmitted at a transmission time when abase station receives signal using a best beam.
 26. The apparatus ofclaim 25, wherein the best beam denotes a beam whose correspondingreference signal, transmitted during the synchronization subframe, is astrongest reference signal at the UE among all possible beams.
 27. Theapparatus of claim 25, wherein the DRACH signal is transmitted in thebest beam selected from a plurality of beams received during thesynchronization subframe.
 28. The apparatus of claim 17, wherein eachattempt is made at a transmission time denoted by a combination of oneor more of frame index, subframe index, or symbol index.
 29. Anapparatus for wireless communication, the apparatus being a basestation, comprising: a memory; and at least one processor coupled to thememory and configured to: combine signals of one or more random-accesschannel (RACH) attempts to decode a RACH signal; and inform a userequipment (UE) regarding a number of RACH attempts used for decoding theRACH signal through a random access response message.
 30. The apparatusof claim 29, wherein, to combine the signals of the one or more RACHattempts, the at least one processor is configured to non-coherently addpower of the signals of the one or more RACH attempts.